Stage device and stage cleaning method

ABSTRACT

A stage device for use in a vacuum includes a frame-shaped movable stage having a sample mounting surface, a fixed stage surrounded by the movable stage, an air bearing to float the movable stage by supplying gas to a gap between the stages, a pressure regulator to regulate a pressure of the gas, a differential pumping portion to prevent the gas from flowing outside the gap, and a controller. The controller moves the movable stage within a predetermined range under a pressure in the differential pumping portion set equal to that for movable stage in use when setting a floating height of the movable stage lower than that for movable stage in use, and under the pressure in the differential pumping portion set higher than that for movable stage in use when setting the floating height of the movable stage equal to that for movable stage in use.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of prior International PatentApplication No. PCT/JP2009/055630, filed Mar. 23, 2009, the entirecontents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a stage device and a stage cleaningmethod. In particular, the present invention relates to a stage devicehaving a function of efficiently cleaning a track surface of a samplestage using an air bearing in a vacuum in an electron beam exposuresystem or the like, and a method of cleaning a stage of the same.

2. Description of the Prior Art

In electron beam exposure systems and electron microscopes, a sample isexposed, observed, or measured while being mounted on a stage. Forexample, an electron beam exposure system performs exposure while movinga stage in accordance with exposure data so that a required position ona wafer may be exposed.

Such stages include cross roller bearing stages. In cross roller bearingstages, rollers in a track between a movable stage and a fixed stagerevolve to move the movable stage. When such stages are in use, oil forvacuum devices is applied to a track and rollers for the lubrication ofthe track and the prevention of particle generation.

When such a stage with a mechanical bearing is used in a state where aparticle exists on a track, the particle causes strain in the stagemechanism. Such strain degrades the operation of stage positiondetection, and makes it difficult to detect a stage position accurately.A particle does not remain at a certain place on the track but moves asthe stage moves. This phenomenon hinders replication of the positionchange of the stage and prediction of a position to which the stage ismoved. Thus, the stage mechanism has difficulty in correcting theposition of the stage. Further, in the case where oil is applied to thetrack, particles can be removed to a certain extent while the oilexists, but the amount of particles may rapidly increase when the oil islost.

In contrast to such stages using mechanical bearings, technologies usingair bearings have been studied and used. For example, Japanese PatentApplication No.2006-66589 describes a stage device in an exposure systemfor use in photolithography. In the stage device, a movable member issupported on a base member in a noncontact manner using a fluid bearing(gas bearing or air bearing).

When such an air bearing is used, the degradation of accuracy of a stagecaused by particles on the track of the stage can be reduced compared towhen a mechanical bearing is used.

However, the stage device is not necessarily always able to preventdegradation of accuracy of the stage for any-sized particles. Forexample, in the case where there is a particle of a size approximatelyequal to the height of the noncontact portion, the particle may beentangled when the stage is moved, and the fixed member and the movablemember may come into contact with each other. When such a situationarises, the attitude of the stage mounted on the movable member becomesunstable. This results in accuracy degradation.

It should be noted that no techniques have been reported for removingparticles in the case where a stage is moved using an air bearingmechanism in a vacuum.

SUMMARY OF THE INVENTION

The present invention has been made in view of the above-describedproblems in the prior art. An object of the present invention is toprovide a stage device and a stage cleaning method which enable toefficiently remove the particles present on a track of a stage using anair bearing in a vacuum.

To achieve the above-described problem in the conventional art,according to a basic embodiment, a stage device for use in an electronbeam exposure system includes: a gas supply unit to generate gas; apressure regulator to regulate a pressure of the gas; a frame-shapedmovable stage having a sample mounting surface; a fixed stage having asurface facing an opposite surface of the movable stage from the samplemounting surface, the fixed stage being surrounded by the movable stage;an air bearing to float the movable stage by supplying the gas to a gapportion between the fixed stage and the movable stage; a differentialpumping portion to prevent the gas from flowing outside the gap portionbetween the movable stage and the fixed stage; and a controller tocontrol the gas supply unit, the pressure regulator, the movable stage,and the differential pumping portion in a cleaning operation and anelectron beam exposure operation, wherein the controller performs thecleaning operation on a track of the air bearing by moving the movablestage within a predetermined range under a pressure in the differentialpumping portion set equal to that for the movable stage in use for theelectron beam exposure operation when a floating height of the movablestage is set lower than that for the movable stage in use for theexposure operation, and by moving the movable stage within apredetermined range under the pressure in the differential pumpingportion set higher than that for the movable stage in use for theelectron beam exposure operation when the floating height of the movablestage is set equal to that for the movable stage in use for the exposureoperation.

According to the embodiment, the stage device further includes: aninterferometer to detect a position of the movable stage, wherein, inthe cleaning operation, the controller may move the movable stage to apredetermined position, set the floating height of the movable stagelower than that for the movable stage in use for the electron beamexposure operation, measure rolling and pitching of the movable stage,and determine that a particle exists on the track of the air bearing ifa value of any of the rolling and pitching exceeds a predeterminedvalue. The stage device further includes: a vertical position detectorto detect a vertical position of the movable stage, wherein, in thecleaning operation, the controller may move the movable stage to apredetermined position, set the floating height of the movable stagelower than that for the movable stage in use for the electron beamexposure operation, detect a change in the vertical position of themovable stage with respect to a change in a pressure for supplying thegas, and determine that a particle exists on the track of the airbearing if the change in the vertical position is out of a predeterminedallowable value range.

Further, in the stage device according to the embodiment, the controllermay move the movable stage from one end of the fixed stage to anopposite end of the fixed stage at least once and reciprocate themovable stage with a short stroke of 10 μm or less around thepredetermined position twice or more.

Additionally, according to another embodiment, there is provided a stagecleaning method for the stage device. The stage cleaning method for astage device for use in a vacuum, the stage device including: a gassupply unit to generate gas; a pressure regulator to regulate a pressureof the gas; a frame-shaped movable stage having a sample mountingsurface; a fixed stage having a surface facing an opposite surface ofthe movable stage from the sample mounting surface, the fixed stagebeing surrounded by the movable stage; an air bearing to float themovable stage by supplying the gas to a gap portion between the fixedstage and the movable stage; and a differential pumping portion toprevent the gas from flowing outside the gap portion between the movablestage and the fixed stage, the method including the steps of: regulatinga floating height of the movable stage and a pressure in thedifferential pumping portion; and moving the movable stage within apredetermined range while maintaining the floating height of the movablestage and the pressure in the differential pumping portion.

In the stage cleaning method according to the another embodiment, thestep of regulating the floating height and the pressure in thedifferential pumping portion may include the steps of: adjusting thepressure in the differential pumping portion to a pressure equal to thatfor the movable stage for normal use of the stage (i.e., electron beamexposure operation) when the floating height is set lower than that forthe movable stage in the normal use; and adjusting the pressure in thedifferential pumping portion to a pressure higher than that for themovable stage in the normal use when the floating height is set equal tothat for the movable stage in the normal use, may include before thestep of adjusting the floating height and the pressure in thedifferential pumping portion, the steps of: moving the movable stage toa predetermined position; setting the floating height of the movablestage lower than that for the movable stage in the normal use andmeasuring rolling and pitching of the movable stage; and determiningthat a particle exists on a track of the air bearing if any of therolling and pitching exceeds a predetermined allowable value, andfurther may include before the step of regulating the floating heightand the pressure in the differential pumping portion, the steps of:moving the movable stage to a predetermined position; setting thefloating height of the movable stage lower than that for the movablestage in the normal use and measuring a vertical position of the movablestage; and determining that a particle exists on a track of the airbearing if a change in the vertical position with respect to a change ina pressure for supplying the gas is out of a predetermined allowablevalue range.

In the stage cleaning method according to the another embodiment, thestep of moving the movable stage within the predetermined range mayincludes the steps of: moving the movable stage to one end of the fixedstage; and moving the movable stage to an opposite end of the fixedstage, and may be the step of reciprocating the movable stage with ashort stroke of 10 μm or less around a predetermined position twice ormore.

In the stage device and stage cleaning method of the present invention,the air supplied to the air bearing is regulated so that the width ofthe gap between the movable stage and the fixed stage becomes smallerthan that for the normal use, and the movable stage is moved within theentire range of the track thereof.

Further, stage cleaning is performed by moving the movable stagethroughout the entire range of the track thereof with the width of thegap between the movable stage and the fixed stage being set to a widthfor normal use and with the pressure on the differential pumping portionof the air bearing being increased.

These make it possible to remove particles present on the track of themovable stage.

Moreover, the pitching and rolling of the movable stage are detected atpredetermined positions with the width of the gap between the movablestage and the fixed stage being narrowed by regulating air supplied tothe air bearing. When the pitching or rolling of the movable stage isdetected, stage cleaning is performed.

Thus, stage cleaning needs to be carried out only when necessary, andefficient stage cleaning can be performed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing the configuration of an electron beamexposure system;

FIG. 2 is a block diagram showing the configuration of a sample stagedevice of an exposure system according to FIG. 1;

FIGS. 3A to 3C are schematic diagrams showing the configuration of aprincipal part, in which an air bearing is used, of the sample stagedevice;

FIGS. 4A to 4C are views (part 1) for explaining cleaning on the trackof the sample stage device;

FIG. 5 is a flowchart (part 1) showing one example of a stage cleaningprocess for the sample stage device;

FIGS. 6A to 6C are views for explaining states in which there is aparticle on the track of the sample stage device;

FIG. 7 is a flowchart (part 1) showing one example of a particledetection process in the stage cleaning process for the sample stagedevice;

FIG. 8 is a flowchart (part 2) showing one example of a particledetection process in the stage cleaning process for the sample stagedevice;

FIGS. 9A to 9C are views (part 2) for explaining cleaning on the trackof the sample stage device;

FIG. 10 is a flowchart (part 2) showing one example of a stage cleaningprocess for the sample stage device;

FIGS. 11A and 11B are views (part 3) for explaining cleaning on thetrack of the sample stage device; and

FIG. 12 is a flowchart (part 3) showing one example of a stage cleaningprocess for the sample stage device.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

(1) First Embodiment

Hereinafter, embodiments of the present invention are described withreference to the drawings. First, the configuration of an electron beamexposure system and a stage device is described with reference to FIGS.1 to 3C. Next, a method of cleaning particles present on the track of asample stage is described with reference to FIGS. 4A to 5. It should benoted that though the following is described by taking the case where astage device is used in an electron beam exposure system, the presentinvention is not limited to this case. It is a matter of course that thepresent invention can be applied to other vacuum devices, e.g., a stagefor an electron microscope.

(Configurations of Electron Beam Exposure System and Stage Device)

FIG. 1 is a schematic diagram showing the configuration of an electronbeam exposure system including a stage device according to thisembodiment.

The electron beam exposure system is broadly divided into an exposureunit 100 and a digital controller 200 to control the exposure unit 100.The exposure unit 100 includes an electron beam generation section 130,a mask deflection section 140, and a substrate deflection section 150.

In the electron beam generation section 130, an electron beam EBgenerated in an electron gun 101 is subjected to the converging actionof a first electromagnetic lens 102, and then passes through arectangular aperture 103 a (first opening) of a beam-shaping mask 103.As a result, the electron beam EB is shaped to have a rectangular crosssection.

The electron beam EB shaped into a rectangular shape is imaged onto asecond beam-shaping mask 106 by a second electromagnetic lens 105 a anda third electromagnetic lens 105 b. The electron beam EB is alsodeflected by a first and second electrostatic deflectors 104 a and 104 bfor variable rectangular shaping and passes through a rectangularaperture 106 a (second opening) of the second beam shaping mask 106. Theelectron beam EB is shaped by the first and second openings.

Then, the electron beam EB is imaged onto a stencil mask 111 by a fourthelectromagnetic lens 107 a and a fifth electromagnetic lens 107 b in themask deflection section 140. The electron beam EB is also deflected bythird and fourth electrostatic deflectors 108 a and 108 b (also referredto as first and second selective deflectors, respectively) toward aspecific pattern P formed in the stencil mask 111, and thecross-sectional shape of the electron beam EB is shaped into the shapeof the pattern P. The pattern is also referred to as a characterprojection (CP) pattern. The electron beam EB is bent to be incident onthe stencil mask 111 parallel to the optical axis by the deflector 108 bdisposed near the fifth electromagnetic lens 107 b.

Incidentally, while the stencil mask 111 is fixed to a mask stage, themask stage is movable in a horizontal plane. For the purpose of using apattern P located outside the deflection range (beam deflection region)of the third and fourth electrostatic deflectors 108 a and 108 b, themask stage is moved so that the pattern P may enter the beam deflectionregion.

A sixth electromagnetic lens 113 disposed under the stencil mask 111 hasa role to make the electron beam EB parallel near a shield 115 by theamount adjustment of the current flowing into the sixth electromagneticlens 113.

The electron beam EB which has passed through the stencil mask 111 isbent back to the optical axis by the deflecting actions of fifth andsixth electrostatic deflectors 112 a and 112 b (also referred to asfirst and second bending back deflectors, respectively). The electronbeam EB is bent by the deflector 112 b disposed near the sixthelectromagnetic lens 113 to be returned to the axis and then travelalong the axis.

The mask deflection section 140 includes first and second correctioncoils 109 and 110 which correct beam deflection aberration produced bythe first to sixth electrostatic deflectors 104 a, 104 b, 108 a, 108 b,112 a, and 112 b.

Then, the electron beam EB passes through an aperture 115 a (roundaperture) of the shield 115 partially constituting the substratedeflection section 150, and is projected onto a substrate by anelectromagnetic projection lens 121. Thus, an image of the pattern ofthe stencil mask 111 is transferred onto the substrate at apredetermined reduction ratio, e.g., a reduction ratio of 1/10.

The substrate deflection section 150 includes seventh and eighthelectromagnetic deflectors 119 and 120 which deflect the electron beamEB so that an image of the pattern of the stencil mask 111 is projectedonto a predetermined position on the substrate.

The substrate deflection section 150 further includes third and fourthcorrection coils 117 and 118 to correct the deflection aberration of theelectron beam EB on the substrate.

The digital controller 200 includes an electron gun control section 202,an electrooptic system control section 203, a mask deflection controlsection 204, a mask stage control section 205, a blanking controlsection 206, a substrate deflection control section 207, and a waferstage control section 208. The electron gun control section 202 controlsthe electron gun 101 to control the acceleration voltage, beamirradiation conditions, and the like of the electron beam EB. Theelectrooptic system control section 203 controls parameters such as theamounts of currents flowing into the electromagnetic lenses 102, 105 a,105 b, 107 a, 107 b, 113, and 121 to adjust the magnifications, focalpoint positions, and the like of electrooptic systems constituting theseelectromagnetic lenses. The blanking control section 206 controls thevoltage applied to a blanking deflector to deflect the electron beam EB,which has been being generated before the start of exposure, onto theshield 115. As a result, the blanking control section 206 prevents theelectron beam EB from being applied onto the substrate before exposure.

The substrate deflection control section 207 controls the voltagesapplied to the seventh and eighth electrostatic deflectors 119 and 120to deflect the electron beam EB onto a predetermined position on thesubstrate. The wafer stage control section 208 moves a substrate 12 in ahorizontal direction by adjusting a drive amount of an actuator 125 sothat the electron beam EB may be applied to a desired position on thesubstrate 12. The above-described sections 202 to 208 arecomprehensively controlled by an integration control system 201 such asa workstation.

FIG. 2 is a block diagram showing the configuration of the stage device,on which a sample is mounted, in the exposure system. The stage devicebasically includes a gas supply unit 21, a pressure regulator 22, awafer stage 23, laser interferometers 24, the actuator 25, and the waferstage control section 208.

The gas supply unit 21 generates and sends out clean dry air (CDA).

The pressure regulator 22 is provided at a certain position in a gasflow path to connect the gas supply unit 21 and a supply port of an airbearing of the wafer stage 23, and adjusts the pressure of gas to besupplied to the air bearing. The pressure regulator 22 is configured toinclude an electro-pneumatic regulator which adjusts the pressure of gasand ejects the gas at a set pressure.

The laser interferometers 24 are disposed at positions facing a sidesurface of the wafer stage 23 and a side surface thereof perpendicularto the foregoing side surface, and measure the position of the waferstage 23 and the attitude (pitching, rolling, and yawing) of the waferstage 23 in two perpendicular directions. A laser interferometer 24 isalso provided above the wafer stage 23 to be used in measuring thevertical position of the wafer stage 23.

The wafer stage control section 208 controls the gas supply unit 21, thepressure regulator 22, and the laser interferometers 24 to detect theposition of the wafer stage 23 with high accuracy. In particular, in thepresent invention, as described later, various kinds of control areperformed by adjusting the pressure of air supplied to the air bearingof the wafer stage 23 so that particles present on the wafer stage 23may be removed.

FIGS. 3A to 3C are schematic diagrams showing the configuration of aprincipal part of a stage, which uses an air bearing, of a sample stagedevice where FIG. 3A is a front view, FIG. 3B is a side view, and FIG.3C is an enlarged front view, respectively, of the principal part.

The sample stage includes a slider (movable stage) 35 and a square shank(fixed stage) 34 which are disposed in a vacuum sample chamber 37. Themovable stage 35 is configured in. the form of a frame to surround thefixed stage 34 as shown in FIG. 3B, and moves along the fixed stage 34.The fixed stage 34 is disposed on a stone surface plate 32 placed onvibration isolation mounts 31, with support rods 33 interposedtherebetween.

FIG. 3C shows an enlarged view of the movable stage 35. The movablestage 35 basically includes air pads 36 and a differential pumpingportion 38. The air pads 36 are used to emit to the fixed stage 34 airsent from the gas supply unit 21 through piping 39. The differentialpumping portion 38 adjusts the pressure of the emitted air so that theemitted air may not flow outside a gap portion between the movable stage35 and the fixed stage 34.

The air pads 36 are made of, for example, an aluminum ceramic or azirconia ceramic, and have openings which determine the distribution ofair.

The pressure of air supplied to the air pads 36 is, for example, 0.5[MPa]. By emitting the air toward the fixed stage 34, the movable stage35 is floated.

The differential pumping portion 38 has exhaust channels 38 a, 38 b, and38 c. By discharging air through the exhaust channels 38 a, 38 b, and 38c, the pressure of air is gradually reduced outward from the gapportion. For example, the air pressure is set to 0.1 [MPa], 400 [Pa],and 1 [Pa] for the exhaust channels 38 a, 38 b, and 38 c, respectively.As a result, the flow of outside air becomes 0.0001 [L/min]. Thus, astate in which air hardly flows is obtained, and a vacuum state can bemaintained.

FIGS. 4A to 4C are views for explaining a stage cleaning process whichis performed in the case where a particle is present on the track of themovable stage 35.

It is assumed that a particle 41 is present on the fixed stage 34 asshown in FIG. 4A. This particle appears when the movable stage 35 isfloated from the fixed stage 34, or is a particle or the like fallen onthe fixed stage 34 after adhering to equipment constituting the samplechamber or equipment in a lens barrel.

The width of the gap between the movable stage 35 and the fixed stage 34is approximately 10 to 5 [μm] during normal use of the stage, i.e., anelectron beam exposure operation. In the case where the height of aparticle is smaller than the width of the gap, no problem occurs duringthe electron beam exposure operation. However, in the case where theheight of a particle is approximately equal to the gap width for thestage in use for the exposure operation, the particle may be entangledduring movement. This may cause bumpy motion during the movement or haltthe movement.

For this reason, in a cleaning operation, the gap between the movablestage 35 and the fixed stage 34 is set to have a width smaller than thatfor the normal use (electron beam exposure operation) to eliminateparticles of such sizes from the track of the movable stage 35. Underthis setting, particles 41 are eliminated by moving the movable stage35.

FIG. 4A shows a state in which the width of the gap between the fixedstage 34 and the movable stage 35 is reduced in the cleaning operationwith the movable stage 35 moved to one end (stroke end) of the fixedstage 34. For the normal exposure operation, the floating height is setto approximately 5 [μm]. On the other hand, for the cleaning operation,the floating height is set to, for example, 1 [μm]. Along with this, thewidth of the gap between the fixed stage 34 and a lower portion of themovable stage 35 becomes greater than that of the normal use (exposure).

FIG. 4B shows a state in which the movable stage 35 is moved to theother end of the fixed stage 34 with the state of air in FIG. 4Amaintained. As shown in FIG. 4B, the particle 41 is pushed and moved toan end portion of the fixed stage 34 by the movement of the movablestage 35. In such movement, the movable stage 34 may be reciprocatedonce or multiple times.

After the cleaning operation described with reference to FIGS. 4A and 4B, as shown in FIG. 4C, the movable stage 35 is moved to a sample stageuse position (e.g., a central position of the fixed stage 34), and thewidth of the gap between the fixed stage 34 and the movable stage 35 isadjusted to a normal width for the electron beam exposure operation.

Incidentally, though the above description has been made on theassumption that the movable stage 35 is moved in only one direction, itis a matter of course that the present invention can be applied tomovement in both X- and Y-directions as in an XY stage.

(Stage Cleaning Method)

FIG. 5 is a flowchart showing one example of a stage cleaning process.

First, in step S11, the slider (movable stage) 35 is moved to a strokeend at one end of the range of stage movement.

Then, in step S12, the floating height of the slider 35 is adjusted tobe lower than the floating height of the slider 35 for normal exposure.This adjustment is performed by reducing the pressure of air supplied tothe air pads 36. By reducing the pressure of air, the width of the gapbetween a lower surface of the slider 35 and an upper surface of thesquare shank (fixed stage) 34 is adjusted to, for example, 2 [μm].

Subsequently, in step S13, the slider 35 is moved within the entirerange of stage movement. The slider 35 located at one end of the rangeof stage movement is moved to the other end stroke and then moved to theoriginal end of the range of stage movement again. This causes particleswhich exist on the track of the air bearing and have heights of morethan 2 [μm] to be pushed by a side portion of the slider 35 and moved tothe vicinity of the square shank 34.

Next, in step S14, the slider 35 is moved to a basic position (center ofthe range of stage movement).

After that, in step S15, the floating height of the slider 35 isadjusted to a height for normal use by controlling the pressureregulator 22.

By the above-described stage cleaning process, particles present belowthe slider 35 are removed. This stage cleaning process may beperiodically executed. When the electron beam exposure is carried outafter this process, errors due to the stage position are eliminated.Thus, it becomes possible to perform the exposure operation with highposition accuracy.

As described above, in the stage device and stage cleaning method ofthis embodiment, air supplied to the air bearing is regulated so thatthe width of the gap between the movable stage 35 and the fixed stage 34may become smaller than that for normal use, and the movable stage 35 ismoved within the entire range of the track thereof.

This makes it possible to remove particles present on the track of themovable stage 35 and larger than the gap width for normal use.

(2) Second Embodiment

A stage device and stage cleaning method according to a secondembodiment has a function of detecting whether or not there is aparticle below the slider 35. If it is determined that there is aparticle, stage cleaning is executed.

(Detection of Particle)

FIGS. 6A to 6C show an example of the case where there is a particlebelow the movable stage 35. FIGS. 6A to 6C show a state in which themovable stage 35 is at a height less than a normal floating height at apredetermined position (central region). FIG. 6A shows the case where aparticle 51 is present at an end portion on the fixed stage 34 and notpresent under the movable stage 35. In this case, the pitching androlling of the movable stage 35 do not occur.

FIG. 6B shows an example in which there is a particle under the movablestage 35. In the case where a particle 51 is present under the movablestage 35 as shown in FIG. 6B, the movable stage 35 turns in thedirection of movement and is inclined due to pitching. Thus, the movablestage 35 does not maintain its horizontal state anymore

FIG. 6C shows an example in which there is a particle under the movablestage 35. The movable stage 35 turns in a direction perpendicular to thedirection of movement and is inclined due to rolling. Thus, the movablestage 35 does not maintain its horizontal state anymore.

The above-described pitching and rolling are measured by the laserinterferometers 24 provided at positions facing side surfaces of themovable stage 35. The laser interferometer 24 facing a side surfaceparallel to the direction of movement detects the state of pitching ofthe movable stage 35, and the laser interferometer 24 facing a sidesurface parallel to a direction perpendicular to the direction ofmovement detects the state of rolling of the movable stage 35.

(Stage Cleaning Method)

FIG. 7 is a flowchart showing one example of a stage cleaning process.

First, in step S21, the slider 35 is moved to predetermined positions.The predetermined positions are, for example, three positions capable ofcovering the entire range of movement of the slider 35. The slider 35 ismoved to one of these three positions.

Then, in step S22, the floating height of the slider 35 is adjusted tobe lower than that for normal use.

Subsequently, in step S23, the rolling and pitching of the stage 35 aremeasured. The rolling and pitching are measured by the laserinterferometers 24.

Next, in step S24, a determination is made as to whether or not therolling or the pitching is in an allowable range. If the rolling or thepitching is not in the range of predetermined allowable values, it isdetermined that there is a particle under the slider 35. Then, in stepS25, a stage cleaning process (cleaning operation) for removing theparticle is executed. As described in the first embodiment, this stagecleaning process is performed by moving the slider 35 throughout theentire range of stage movement.

On the other hand, if the rolling or the pitching is within the range ofthe predetermined values, a particle, if present, does not adverselyaffect the movement of the stage device using the air bearing.Accordingly, it is determined that there is no particle at that positionof the slider 35, and the process goes to step S26.

Then, in step S26, determination is made as to whether or not therolling and pitching of the stage have been measured for all thepredetermined positions. If the rolling and pitching of the stage havenot been measured for all the predetermined positions, the processreturns to step S21 to repeat the above process for other positions Ifthe rolling and pitching of the stage have been measured for all thepredetermined positions, no stage cleaning is needed, and this particledetection and stage cleaning process is terminated.

Incidentally, the vertical position of the stage, instead of the rollingand pitching of the stage, may be detected to determine whether or notthere is a particle.

FIG. 8 is a flowchart showing one example of a particle detectionprocess which is performed in the case where the vertical position isdetermined.

First, in step S31, the slider 35 is moved to predetermined positions.The predetermined positions are, for example, three positions capable ofcovering the entire range of movement of the slider 35. The slider 35 ismoved to one of these three positions.

Then, in step S32, the floating height of the slider 35 is adjusted tobe lower than that for normal use.

Subsequently, in step S33, the vertical position of the stage (slider35) is measured. The vertical position of the stage is measured by, forexample, the laser interferometer 24 disposed above the slider 35.

Next, in step S34, a calculation is made of the amount of change in thevertical height of the slider 35 with respect to the floating height ofthe slider 35. A calculation is made of the difference between thevertical position of the slider 35 for normal use and the verticalposition of the slider 35 in the case of the lowered floating height.

Then, in step S35, a determination is made as to whether or not theamount of change is in an allowable range. For example, in the casewhere the floating height is set to a height which is d [μm] lower thanthat for the normal use of the stage, i.e., the exposure operation, ifthe amount of change in the vertical position of the slider 35 is also d[μm], it is determined that the slider 35 is correctly lowered. On theother hand, if the amount of change is smaller than d [μm], it isdetermined that there is some obstacle in the gap between the slider 35and the fixed stage 34. If the amount of change is not in the range ofpredetermined allowable values, it is determined that there is aparticle under the slider 35. Then, in step S36, a stage cleaningprocess for removing the particle is executed. As described in the firstembodiment, this stage cleaning process is performed by moving theslider 35 throughout the entire range of stage movement.

On the other hand, if the amount of change in the vertical position ofthe slider 35 is in the range of the predetermined values, a particle,if present, does not adversely affect the movement of the stage deviceusing the air bearing. Accordingly, it is determined that there is noparticle at that position of the slider 35, and the process goes to stepS37.

Then, in step S37, a determination is made as to whether or not thevertical position of the stage has been measured for all thepredetermined positions. If the vertical position of the stage has notbeen measured for all the predetermined positions, the process returnsto step S31 to repeat the above process for other positions. If thevertical position of the stage has been measured for all thepredetermined positions, no stage cleaning is needed, and this particledetection and stage cleaning process is terminated.

As described above, in the stage device and stage cleaning method ofthis embodiment, the pitching and rolling of the movable stage 35 or achange in the vertical position of the movable stage 35 is detected atpredetermined positions with the width of the gap between the movablestage 35 and the fixed stage 34 being narrowed by regulating airsupplied to the air bearing. When the pitching or rolling of the movablestage 35 is detected, or when a change in the vertical position of themovable stage 35 is detected, stage cleaning is performed.

As a result, stage cleaning only needs to be carried out when necessary,and efficient stage cleaning can be performed.

(3) Third Embodiment

A third embodiment provides a technique adapted to the case where thereis a particle which has adhered to the stage so firmly and thus isunremovable by the process of the first embodiment.

FIGS. 9A to 9C are views for explaining a stage cleaning process whichis performed in the case where a particle is present under the movablestage 35.

In the case where a particle which has adhered to the fixed stage 34,the particle may be incapable of being completely removed by a methodsuch as described for the first embodiment in which a particle is pushedout to an end portion of the fixed stage 34 by the movable stage 35,thus remaining on the track. In this case, when the remaining particleis left as it is, the remaining particle may be overlaid with anotherparticle. This may cause a problem during the normal use, i.e., theelectron beam exposure operation.

To cope with this, at a position where there is such an adheringparticle, the particle is eliminated by making the particle small.

FIG. 9B shows a state in which the movable stage 35 is twice or morereciprocated back and forth in the direction of movement with a shortstroke, e.g., a stroke of 10 μm while the condition of air in FIG. 9A ismaintained. By reciprocating the movable stage 35 twice or more, aparticle 61 a is crushed to be as small as particles 61 b and 61 c. Thisreciprocating motion is performed until the movable stage 35 becomeshorizontal as shown in FIG. 9C.

Whether or not the movable stage 35 becomes horizontal is determined bydetecting the attitude of the movable stage 35 using the laserinterferometer 24 and making sure that pitching and rolling do notoccur.

(Stage Cleaning Method)

FIG. 10 is a flowchart showing another example of a stage cleaningprocess.

First, in step S41, the slider 35 is moved to a predetermined position.

Then, in step S42, the floating height of the slider (movable stage) 35is adjusted to be lower than that for the normal use (electron beamexposure).

Subsequently, in step S43, the slider is reciprocated with apredetermined short stroke twice or more.

Next, in step S44, a determination is made as to whether or not theprocessing has been finished for all predetermined positions. If theprocessing has been finished for all the predetermined positions, theprocess goes to step S45. If the processing has not been finished forall the predetermined positions, the process goes to step S41 to repeatthe above process for the remaining positions.

Then, in step S45, the slider 35 is moved to a basic position.

Subsequently, in step S46, the floating height of the slider 35 isadjusted to be a height for normal use, and this stage cleaning processis terminated.

Incidentally, the stage cleaning process described for the thirdembodiment may be performed after the particle detection described forthe second embodiment. In this case, the stage cleaning process shown inFIG. 10 is executed in the “execution of stage cleaning” in step S25 ofFIG. 7 or step S36 of FIG. 8.

As described above, in the stage device and stage cleaning method ofthis embodiment, the movable stage 35 is reciprocated twice or morewithin a short distance at a position where there is a particle.

This makes it possible to crush a particle adhering to the fixed stage34 or the movable stage 35 and to remove a particle present on the trackof the air bearing.

(4) Fourth Embodiment

In a fourth embodiment, a particle present on the fixed stage 34 isremoved using air for use in the air bearing.

FIG. 11A shows a state in which there is a particle 71 under the movablestage 35. Air supplied to the air bearing is used to remove such aparticle from the track of the movable stage 35.

The differential pumping portion 38 is a mechanism for graduallyreducing the pressure of air emitted from the air pads 36 so that theair may not flow outside the gap portion between the movable stage 35and the fixed stage 34. In this embodiment, the pressure placed on thedifferential pumping portion 38 is adjusted to a high pressure to causethe air to flow outside. For example, air is sucked through exhaustchannels 72 a, 72 b, and 72 c into piping 73 as shown in FIG. 11B, andthe pressure at the differential pumping portion 38 is increased to behigher than that for the normal use (electron beam exposure operation)by reducing the suction force.

Thus, particles present in the vicinities of both ends of the movablestage 35 are blown away from the gap to the outside. In this state, bymoving the movable stage 35 from one end to the other end, particlespresent on the track are pushed out and moved to end portions of thefixed stage 34.

Incidentally, in this case, since the air in a last stage is emitted,the pressure in a vacuum chamber is increased. Accordingly, it isnecessary to isolate an electron gun, which is an electron beam source,in terms of vacuum. Further, since the suction force of each exhaustchannel is reduced to increase the pressure of differential pumping to apressure higher than that for the normal use, i.e., the electron beamexposure operation, particles may flow back from the piping 73 connectedto the exhaust channels. Accordingly, it is desirable that a filter forparticle back-flow prevention be provided in the piping 73 of thedifferential pumping portion 38 at a position near the gap portion.

(Stage Cleaning Method)

FIG. 12 is a flowchart showing another example of a stage cleaningprocess.

First, in step S51, the slider 35 is moved to a stroke end at one end ofthe range of stage movement.

Then, in step S52, the floating height of the slider 35 is adjusted tothat for the normal use. In this adjustment, the floating height isadjusted to, for example, 5 [μm] by setting the pressure of air suppliedto the air pads 36 to a pressure for the normal use.

Subsequently, in step S53, the pressure in the differential pumpingportion 38 is increased to be higher than that for the normal use. Inthe normal use, the pressure of air is gradually reduced fromatmospheric pressure to 10⁻⁴ [Pa] by the differential pumping portion 38to prevent the air from flowing out. On the other hand, the suctionforces of the exhaust channels 72 a to 72 c are adjusted to allow theair to have such a pressure that the air flows to the outside.

Next, in step S54, the slider 35 is moved throughout the entire range ofstage movement. The slider 35 located at one end of the range of stagemovement is moved to the other end stroke and then moved to the originalend of the range of stage movement again. Thus, particles present on thetrack of the air bearing are blown away by the air to be removed fromthe course.

Then, in step S55, the slider 35 is moved to a basic position.

Subsequently, in step S56, the pressure in the differential pumpingportion 38 is adjusted to a pressure for normal use, and this stagecleaning process is terminated.

Incidentally, the stage cleaning process described for the fourthembodiment may be performed after the particle detection described forthe second embodiment. In this case, the stage cleaning process shown inFIG. 12 is executed in the “execution of stage cleaning” in step S25 ofFIG. 7 or step S36 of FIG. 8.

As described above, in the stage device and stage cleaning method ofthis embodiment, stage cleaning is performed by moving the movable stage35 throughout the entire range of the track thereof with the width ofthe gap between the movable stage 35 and the fixed stage 34 being set toa width for the normal use (electron beam exposure operation) of thestage device and with the pressure on the differential pumping portion38 of the air bearing being increased.

This makes it possible to remove particles present on the track of themovable stage 35.

It should be noted that the present invention is a patent application(patent application to which Article 19 of the Industrial TechnologyEnhancement Act of Japan is applied) pertaining to the result ofresearch (research in a project named “Development of ComprehensiveOptimization Technologies to Improve Mask Design, Drawing andInspection,” entrusted by New Energy and Industrial TechnologyDevelopment Organization in fiscal year 2008) entrusted by the Japanesenational government or the like.

1. A stage device for use in an electron beam exposure system, comprising: a gas supply unit to generate gas; a pressure regulator to regulate a pressure of the gas; a frame-shaped movable stage having a sample mounting surface; a fixed stage having a surface facing an opposite surface of the movable stage from the sample mounting surface, the fixed stage being surrounded by the movable stage; an air bearing to float the movable stage by supplying the gas to a gap portion between the fixed stage and the movable stage; a differential pumping portion to prevent the gas from flowing outside the gap portion between the movable stage and the fixed stage; and a controller to control the gas supply unit, the pressure regulator, the movable stage, and the differential pumping portion, in a cleaning operation and in an electron beam exposure operation; wherein the controller controls the cleaning operation by moving the movable stage within a predetermined range and regulating the pressure of the gas supplied to the air bearing via the pressure regulator; and wherein the floating height of the movable stage in the cleaning operation is set lower than that in the electron beam exposure operation and the pressure in the differential pumping portion in the cleaning operation is set equal to that in the electron beam exposure operation, or the floating height of the movable stage in the cleaning operation is set equal to that in electron beam exposure operation and the pressure in the differential pumping portion in the cleaning operation is set higher than that in the electron beam exposure operation.
 2. The stage device according to claim 1, further comprising: an interferometer to detect a position of the movable stage, wherein, in the cleaning operation, rolling and pitching of the movable stage is measured based on the position detected by the interferometer and it is determined that a particle exists on the track of the air bearing if a value of any of the rolling and pitching exceeds a predetermined value.
 3. The stage device according to claim 2, further comprising: a vertical position detector to detect a vertical position of the movable stage, wherein, in the cleaning operation, a change in the vertical position of the movable stage with respect to a change in a pressure for supplying the gas is measured based on the vertical position detected by the vertical position detector and it is determined that a particle exists on the track of the air bearing if the change in the vertical position is out of a predetermined allowable value range.
 4. The stage device according to claim 1, wherein the controller is configured to move the movable stage from one end of the fixed stage to an opposite end of the fixed stage at least once in the cleaning operation.
 5. The stage device according to claim 1, wherein the controller is configured to reciprocate the movable stage with a short stroke of 10 μm or less around the predetermined position twice or more in the cleaning operation.
 6. The stage device according to claim 1, further comprising a back-flow prevention filter in piping of the differential pumping portion on a side near the gap portion. 